The present invention relates to electrical machinery fabricated from high-silicon steel sheets or ribbons produced by the rapid quenching or melt-spinning process and more particularly magnetic cores thereof.
High-silicon steel sheets or ribbons which are readily available in the market and contain about 3% Si (silicon) have been widely used in the fabrication of magnetic cores of power transformers. The magnetic cores made of especially oriented silicon steel sheets or ribbons with the crystal texture described by the crystal plane (110) and the ribbon long axes [001] have the lowest iron or core loss. Extensive investigations have been made in order to improve the properties of such silicon steels, so that it now becomes almost impossible to reduce the core loss with such silicon steels. However, the iron loss of magnetic cores used at present is still considerable, and in view of energy savings it is a matter of national importance to reduce the core loss. From the standpoint of physical properties of silicon steels, it is preferable to increase the silicon content to, for instance, 6.5% because the intrinsic electric resistivity is increased, the magnetocrystalline anisotropy is decreased, and the magnetostriction becomes zero, so that the iron loss can be remarkably reduced and reduction in noise can be expected. Even though the physical properties can be improved with increase in Si content as described above, one of the very important mechanical properties; that is, ductility, is considerably adversely affected. As a result, it has been extremely difficult or almost impossible to mass produce sheets of such high-silicon steels by conventional rolling.
However, recently the rapid quenching or melt-spinning process has been developed. According to the rapid quenching or melt-spinning process, a molten alloy is made to squirt through a small opening or nozzle onto the surface of a cylinder or disk rotating at an extremely high velocity. The melt of alloy on the surface of the cylinder or disk cools and solidifies very quickly and is drawn into a ribbon. The underlying principle of this process is to cool or solidify the molten alloy at an extremely high cooling rate of 10.sup.5 .degree. to 10.sup.6 .degree. C./sec. As a consequence, the alloy in the liquid state above a liquid temperature is rapidly solidified so that thus prepared alloy is considerably smaller in grain size than the alloys produced by the conventional casting processes and consequently it has a higher degree of ductility even when it contains as much as 6.5% Si. In addition, as compared with the conventional processes for the production of sheet metal through alternate steps of rolling and heat treatment, the rapid quenching or melt-spinning process has a distinctive advantage in that sheet metal can be drawn by a single step and therefore is suitable for mass production of sheet metal.
The inventors prepared various high-silicon steels containing 5-8% Si by the rapid quenching or melt-spinning process and made extensive studies and experiments of their crystal textures. The results of investigation show that the surfaces of such ribbons have the (100) crystal plane, but do not have the zone axes [001] of the longitudinal or axial ribbon direction; that is, they are isotropic in the plane or have the crystal texture which can be described with (100)[0 kl]. Therefore, such ribbon as described above can find various interesting applications in many fields. However, in case such ribbon is used as, for instance, a toroidal magnetic core of a power transformer and the directions of the magnetic fluxes coincide with the longitudinal direction of the sheet, the direction of the magnetic fluxes do not coincide with the magnetic easy direction of the ribbon. Accordingly, the iron losses of the sheet become larger than those of the oriented silicon steel ribbons in which the directions of the magnetic fluxes coincide with the magnetic easy direction &lt;001&gt; of the ribbons.